Polishing composition for nickel-phosphorous-coated memory disks

ABSTRACT

The invention provides a chemical-mechanical polishing composition containing wet-process silica, an oxidizing agent that oxidizes nickel-phosphorous, a chelating agent, polyvinyl alcohol, and water. The invention also provides a method of chemically-mechanically polishing a substrate, especially a nickel-phosphorous substrate, by contacting a substrate with a polishing pad and the chemical-mechanical polishing composition, moving the polishing pad and the polishing composition relative to the substrate, and abrading at least a portion of the substrate to polish the substrate.

BACKGROUND OF THE INVENTION

The demand for increased storage capacity in memory or rigid disks andthe trend towards miniaturization of memory or rigid disks (due to therequirement for smaller hard drives in computer equipment) continues toemphasize the importance of the memory or rigid disk manufacturingprocess, including the planarization or polishing of such disks forensuring maximal performance. While there exist severalchemical-mechanical polishing (CMP) compositions and methods for use inconjunction with semiconductor device manufacture, few conventional CMPmethods or commercially available CMP compositions are well-suited forthe planarization or polishing of memory or rigid disks.

As the demand for increased storage capacity has increased, so has theneed for improved processes for the polishing of such memory or rigiddisks. The term “memory or rigid disk” refers to any magnetic disk, harddisk, rigid disk, or memory disk for retaining information inelectromagnetic form. The memory or rigid disk typically has a surfacethat comprises nickel-phosphorus, but the memory or rigid disk surfacecan comprise any other suitable material. The planarity of the memory orrigid disks must be improved, as the distance between the recording headof a disk drive and the surface of the memory or rigid disk hasdecreased with improvements in recording density that demand a lowerflying height of the magnetic head with respect to the memory or rigiddisk. In order to permit a lower flying height of the magnetic head,improvements to the surface finish of the memory or rigid disk arerequired.

Improvements to the surface finish of the memory or rigid disk requirethat scratches and micro defects caused by abrasive particles must bereduced. It has been hypothesized that frictional forces generatedbetween a polishing pad and a substrate being polished leads toincreased scratching and micro defects. However, the presence ofadditives intended to reduce frictional forces typically lead toagglomeration of abrasive particles, with a consequent increase inscratching and micro defects. Accordingly, there is a need in the artfor polishing compositions exhibiting reduced scratching and microdefects and also exhibiting good surface topography and practicableremoval rates.

BRIEF SUMMARY OF THE INVENTION

The invention provides a method of chemically-mechanically polishing asubstrate, which method comprises (i) providing a substrate comprisingat least one layer of nickel-phosphorous, (ii) providing a polishingpad, (iii) providing a polishing composition comprising (a) wet-processsilica, (b) an oxidizing agent that oxidizes nickel-phosphorous, (c) achelating agent, (d) polyvinyl alcohol, (c) water, wherein the polishingcomposition has a pH of about 1 to about 4, (iv) contacting a surface ofthe substrate with the polishing pad and the polishing composition, and(v) abrading at least a portion of the surface of the substrate toremove at least some nickel-phosphorous from the surface of thesubstrate and to polish the surface of the substrate.

The invention also provides a chemical-mechanical polishing compositioncomprising (a) wet-process silica, (b) an oxidizing agent that oxidizesnickel-phosphorous, (c) a chelating agent, (d) polyvinyl alcohol,wherein the polyvinyl alcohol has a molecular weight of about 8,000g/mol to about 50,000 g/mol, (c) water, wherein the polishingcomposition has a pH of about 1 to about 4, and wherein the polishingcomposition does not comprise a heterocyclic compound.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a chemical-mechanical polishing compositioncomprising, consisting essentially of, or consisting of (a) wet-processsilica, (b) an oxidizing agent that oxidizes nickel-phosphorous, (c) achelating agent, (d) polyvinyl alcohol, wherein the polyvinyl alcoholhas a molecular weight of about 8,000 g/mol to about 50,000 g/mol, (c)water, wherein the polishing composition has a pH of about 1 to about 4.

The polishing composition comprises wet-process silica particles (e.g.,condensation-polymerized or precipitated silica particles). Preferably,the wet-process silica particles are condensation-polymerized silicaparticles. Condensation-polymerized silica particles typically areprepared by condensing Si(OH)₄ to form colloidal particles, wherecolloidal is defined as having an average particle size between about 1nm and about 1000 nm. Such abrasive particles can be prepared inaccordance with U.S. Pat. No. 5,230,833 or can be obtained as any ofvarious commercially available products, such as the Akzo-Nobel Bindzil50/80 product and the Nalco 1050, 1060, 2327, and 2329 products, as wellas other similar products available from DuPont, Bayer, AppliedResearch, Nissan Chemical, Fuso, and Clariant. Other examples ofsuitable wet-process silica include but are not limited to XP320, XP442,CC-301, and CC401 (EKA, Mannheim, Germany), N1115, N8691, N1030C, andN8699 (supplied by Nalco Co., Naperville, Ill.), ST-N and ST-0 (NissanChemical America, Houston, Tex.), and Nexsil 20, 20A, 12, 8, and 5(Nyacol Nano Technologies, Ashland, Mass.).

The silica particles can have any suitable average particle size (i.e.,average particle diameter). The silica particles can have an averageparticle size of about 10 nm or more, e.g., about 15 nm or more, about20 nm or more, or about 25 nm or more. Alternatively, or in addition,the silica can have an average particle size of about 80 nm or less,e.g., about 75 nm or less, about 70 nm or less, about 60 nm or less,about 50 nm or less, about 40 nm or less, or about 30 nm or less. Thus,the silica can have an average particle size bounded by any two of theabove endpoints. For example, the silica can have an average particlesize of about 10 nm to about 80 nm, about 10 nm to about 70 nm, about 10nm to about 60 nm, about 10 nm to about 50 nm, about 10 nm to about 40nm, about 10 nm to about 30 nm, about 20 nm to about 80 nm, about 20 nmto about 60 nm, about 20 nm to about 40 nm, or about 20 nm to about 30nm.

The polishing composition can comprise any suitable amount of silica.Typically, the polishing composition can contain about 0.01 wt. % ormore, e.g., about 0.05 wt. % or more, about 0.1 wt. % or more, about 0.5wt. % or more, or about 1 wt. % or more of silica. Alternatively, or inaddition, the polishing composition can contain about 10 wt. % or less,e.g., about 9 wt. % or less, about 8 wt. % or less, about 7 wt. % orless, about 6 wt. % or less, or about 5 wt. % or less of silica. Thus,the polishing composition can comprise silica in amounts bounded by anytwo of the above endpoints recited for silica. For example the polishingcomposition can comprise about 0.01 wt. % to about 10 wt. %, about 0.5wt. % to about 10 wt. %, 1 wt. % to about 10 wt. %, 0.5 wt. % to about10 wt. %, 0.5 wt. % to about 9 wt. %, 0.5 wt. % to about 8 wt. %, 0.5wt. % to about 7 wt. %, 0.5 wt. % to about 6 wt. %, 0.5 wt. % to about 5wt. %, or 1 wt. % to about 5 wt. % of silica.

The abrasive particles preferably are colloidally stable. The termcolloid refers to the suspension of abrasive particles in the liquidcarrier. Colloidal stability refers to the maintenance of thatsuspension through time. In the context of this invention, an abrasiveis considered colloidally stable if, when the abrasive is placed into a100 ml graduated cylinder and allowed to stand unagitated for a time of2 hours, the difference between the concentration of particles in thebottom 50 ml of the graduated cylinder ([B] in terms of g/ml) and theconcentration of particles in the top 50 ml of the graduated cylinder([T] in terms of g/ml) divided by the initial concentration of particlesin the abrasive composition ([C] in terms of g/ml) is less than or equalto 0.5 (i.e., {[B]−[T]}/[C]≦0.5). More preferably, the value of[B]−[T]/[C] is less than or equal to 0.3, and most preferably is lessthan or equal to 0.1.

The polishing composition comprises an oxidizing agent that oxidizesnickel-phosphorous. Preferred oxidizing agents are selected from thegroup consisting of hydrogen peroxide, urea hydrogen peroxide,peroxysulfuric acid, peroxyacetic acid, perboric acid, salts thereof,and combinations thereof. More preferably, the oxidizing agent ishydrogen peroxide. Typically, the polishing composition can containabout 0.5 wt. % or more, e.g., about 1 wt. % or more, or about 2 wt. %or more, of the oxidizing agent that oxidizes nickel-phosphorous.Alternatively, or in addition, the polishing composition can containabout 10 wt. % or less, e.g., about 8 wt. % or less, or about 6 wt. % orless, or about 4 wt. % or less, of the oxidizing agent that oxidizesnickel-phosphorous. Thus, the polishing composition can comprise silicain amounts bounded by any two of the above endpoints recited for theoxidizing agent that oxidizes nickel-phosphorous. For example thepolishing composition can comprise about 0.5 wt. % to about 10 wt. %, orabout 1 wt. % to about 8 wt. %, or about 2 wt. % to about 6 wt. % of theoxidizing agent that oxidizes nickel-phosphorous.

The polishing composition comprises a chelating agent. Desirably, thechelating agent is a chelating agent for nickel. The chelating agent canbe any suitable chelating agent, especially any suitable chelating agentfor nickel. The chelating agent preferably is chosen so that thepolishing composition exhibits low dissolution behavior when in contactwith a substrate comprising nickel-phosphorous. Non-limiting examples ofsuitable chelating agents include glycine and alanine. In a preferredembodiment, the chelating agent is glycine.

Typically, the polishing composition can contain about 0.1 wt. % ormore, e.g., about 0.2 wt. % or more, or about 0.3 wt. % or more, orabout 0.4 wt. % or more, or about 0.5 wt. % or more, of the chelatingagent. Alternatively, or in addition, the polishing composition cancontain about 2 wt. % or less, e.g., about 1.8 wt. % or less, or about1.6 wt. % or less, or about 1.4 wt. % or less, or about 1.2 wt. % orless, or about 1 wt. % or less, of the chelating agent. Thus, thepolishing composition can comprise the chelating agent in amountsbounded by any two of the above endpoints recited for the chelatingagent. For example the polishing composition can comprise about 0.1 wt.% to about 2 wt. %, or about 0.2 wt. % to about 1.8 wt. %, or about 0.3wt. % to about 1.6 wt. %, about 0.4 wt. % to about 1.4 wt. %, or about0.5 wt. % to about 1.2 wt. % of the chelating agent.

The polishing composition comprises polyvinyl alcohol. The polyvinylalcohol can be any suitable polyvinyl alcohol. In some embodiments, thepolyvinyl alcohol has a molecular weight of about 8,000 g/mol or more,e.g., about 10,000 g/mol or more, about 12,000 g/mol or more, or about13,000 g/mol or more. In some embodiments, alternatively, or inaddition, the polyvinyl alcohol has a molecular weight of about 50,000g/mol or less, e.g., about 45,000 g/mol or less, or about 40,000 g/molor less, or about 35,000 g/mol or less, or about 30,000 g/mol or less,about 25,000 g/mol or less, or about 23,000 g/mol or less. Thus, in someembodiments, the polyvinyl alcohol has a molecular weight bounded by anytwo of the above endpoints recited for the polyvinyl alcohol. Forexample the polyvinyl alcohol can have a molecular weight of about 8,000g/mol to about 50,000 g/mol, about 10,000 g/mol to about 45,000 g/mol,about 10,000 g/mol to about 40,000 g/mol, about 10,000 g/mol to about35,000 g/mol, about 10,000 g/mol to about 30,000 g/mol, about 12,000g/mol to about 25,000 g/mol, or about 13,000 g/mol to about 23,000g/mol.

The polyvinyl alcohol can have any suitable degree of hydrolysis.Typically, polyvinyl alcohol has a degree of hydrolysis of about 90% ormore, or about 92% or more, or about 94% or more, or about 96% or more,or about 98% or more. As is well known in the art, polyvinyl alcohol istypically prepared by hydrolysis of polyvinyl acetate. The degree ofhydrolysis refers to the percentage of acetate groups in the polyvinylacetate that have been hydrolyzed. In other words, the degree ofhydrolysis refers to the percentage of free hydroxyl groups present inthe polyvinyl alcohol.

Typically, the polishing composition can contain about 0.1 wt. % ormore, e.g., about 0.2 wt. % or more, or about 0.3 wt. % or more, orabout 0.4 wt. % or more, or about 0.5 wt. % or more, of polyvinylalcohol. Alternatively, or in addition, the polishing composition cancontain about 2 wt. % or less, e.g., about 1.8 wt. % or less, or about1.6 wt. % or less, or about 1.4 wt. % or less, or about 1.2 wt. % orless, or about 1 wt. % or less, of polyvinyl alcohol. Thus, thepolishing composition can comprise polyvinyl alcohol in amounts boundedby any two of the above endpoints recited for polyvinyl alcohol. Forexample the polishing composition can comprise about 0.1 wt. % to about2 wt. %, or about 0.2 wt. % to about 1.8 wt. %, or about 0.3 wt. % toabout 1.6 wt. %, or about 0.4 wt. % to about 1.4 wt. %, or about 0.5 wt.% to about 1.2 wt. % of polyvinyl alcohol.

Typically, the polishing composition has a pH of about 1 or more, e.g.,about 2 or more, or about 3 or more. Alternatively, or in addition, thepolishing composition has a pH of about 4 or less, e.g., about 3 orless, or about 2 or less. Thus, the polishing composition has a pHbounded by any two of the above endpoints recited for the pH of thepolishing composition. For example, the polishing composition can have apH of about 1 to about 4, about 1 to about 3, about 2 to about 4, about3 to about 4, or about 1 to about 2.

In certain embodiments, the polishing composition does not comprise aheterocyclic compound. More particularly, the polishing compositionsubstantially comprises less than about 100 ppb (parts per billion),e.g., less than about 75 ppb, or less than about 50 ppb, less than about25 ppb, less than about 5 ppb, or less than about 1 ppb, of anyheterocyclic compounds. In some embodiments, the polishing compositioncontains an undetectable amount of heterocycle compounds. In particular,heterocyclic compounds that complex with copper on the surface of acopper substrate to form an insoluble complex on the surface of thecopper substrate are excluded from the polishing composition of theinvention. Non-limiting examples of specific heterocyclic compounds thatare excluded from the polishing composition of the invention include5-aminotetrazole, imidazole, benzotriazole, benzimidazole, triazole,tolyltriazole, quinaldinic acid, quinolinic acid, amino compounds, iminocompounds, carboxy compounds, mercapto compounds, nitro compounds, ureacompounds, and thiourea compounds, and derivatives thereof. Desirably,the polishing composition does not contain any heterocyclic compounds.

The polishing composition can be prepared by any suitable technique,many of which are known to those skilled in the art. The polishingcomposition can be prepared in a batch or continuous process. Generally,the polishing composition can be prepared by combining the componentsthereof in any order. The term “component” as used herein includesindividual ingredients (e.g., wet-process silica, oxidizing agent thatoxidizes nickel-phosphorous, chelating agent, polyvinyl alcohol, etc.)as well as any combination of ingredients (e.g., wet-process silica,oxidizing agent that oxidizes nickel-phosphorous, chelating agent,polyvinyl alcohol, etc.).

For example, the wet-process silica can be dispersed in water. Thechelating agent and polyvinyl alcohol can then be added, and mixed byany method that is capable of incorporating the components into thepolishing composition. The oxidizing agent that oxidizesnickel-phosphorous can be added at any time during the preparation ofthe polishing composition. The polishing composition can be preparedprior to use, with one or more components, such as the oxidizing agentthat oxidizes nickel-phosphorous, added to the polishing compositionjust before use (e.g., within about 1 minute before use, or within about1 hour before use, or within about 7 days before use). The polishingcomposition also can be prepared by mixing the components at the surfaceof the substrate during the polishing operation.

The polishing composition can be supplied as a one-package systemcomprising wet-process silica, oxidizing agent that oxidizesnickel-phosphorous, chelating agent, polyvinyl alcohol, and water.Alternatively, the wet-process silica can be supplied as a dispersion inwater in a first container, and chelating agent and polyvinyl alcoholcan be supplied in a second container, either in dry form, or as asolution or dispersion in water. The oxidizing agent that oxidizesnickel-phosphorous desirably is supplied separately from the othercomponents of the polishing composition and is combined, e.g., by theend-user, with the other components of the polishing composition shortlybefore use (e.g., 1 week or less prior to use, 1 day or less prior touse, 1 hour or less prior to use, 10 minutes or less prior to use, or 1minute or less prior to use). The components in the first or secondcontainer can be in dry form while the components in the other containercan be in the form of an aqueous dispersion. Moreover, it is suitablefor the components in the first and second containers to have differentpH values, or alternatively to have substantially similar, or evenequal, pH values. Other two-container, or three or more-container,combinations of the components of the polishing composition are withinthe knowledge of one of ordinary skill in the art.

The polishing composition of the invention also can be provided as aconcentrate which is intended to be diluted with an appropriate amountof water prior to use. In such an embodiment, the polishing compositionconcentrate can comprise the wet-process silica, chelating agent,polyvinyl alcohol, and water, with or without the oxidizing agent thatoxidizes nickel-phosphorous, in amounts such that, upon dilution of theconcentrate with an appropriate amount of water, and the oxidizing agentthat oxidizes nickel-phosphorous if not already present in anappropriate amount, each component of the polishing composition will bepresent in the polishing composition in an amount within the appropriaterange recited above for each component. For example, the wet-processsilica, chelating agent, and polyvinyl alcohol can each be present inthe concentration in an amount that is about 2 times (e.g., about 3times, about 4 times, or about 5 times) greater than the concentrationrecited above for each component so that, when the concentrate isdiluted with an equal volume of (e.g., 2 equal volumes of water, 3 equalvolumes of water, or 4 equal volumes of water, respectively), along withthe oxidizing agent that oxidizes nickel-phosphorous in a suitableamount, each component will be present in the polishing composition inan amount within the ranges set forth above for each component.Furthermore, as will be understood by those of ordinary skill in theart, the concentrate can contain an appropriate fraction of the waterpresent in the final polishing composition in order to ensure that othercomponents are at least partially or fully dissolved in the concentrate.

The invention also provides a method of chemically-mechanicallypolishing a substrate with the polishing composition described herein.In particular, the inventive method comprises (i) contacting a substratewith a polishing pad and the chemical-mechanical polishing compositiondescribed herein, (ii) moving the polishing pad relative to thesubstrate with the chemical-mechanical polishing compositiontherebetween, and (iii) abrading at least a portion of the substrate topolish the substrate.

The substrate to be polished using the method of the invention can beany suitable substrate, especially a substrate that containsnickel-phosphorous. A preferred substrate comprises at least one layer,especially an exposed layer for polishing, comprising, consistingessentially of, or consisting of nickel-phosphorous. Particularlysuitable substrates include, but are not limited to, memory or rigiddisks, such as aluminum disks coated with nickel-phosphorous.

The polishing method of the invention is particularly suited for use inconjunction with a chemical-mechanical polishing (CMP) apparatus.Typically, the apparatus comprises a platen, which, when in use, is inmotion and has a velocity that results from orbital, linear, or circularmotion, a polishing pad in contact with the platen and moving with theplaten when in motion, and a carrier that holds a substrate to bepolished by contacting and moving relative to the surface of thepolishing pad. The polishing of the substrate takes place by thesubstrate being placed in contact with the polishing pad and thepolishing composition of the invention and then the polishing pad movingrelative to the substrate, so as to abrade at least a portion of thesubstrate to polish the substrate.

A substrate can be planarized or polished with the chemical-mechanicalpolishing composition with any suitable polishing pad (e.g., polishingsurface). Suitable polishing pads include, for example, woven andnon-woven polishing pads. Moreover, suitable polishing pads can compriseany suitable polymer of varying density, hardness, thickness,compressibility, ability to rebound upon compression, and compressionmodulus. Suitable polymers include, for example, polyvinylchloride,polyvinylfluoride, nylon, fluorocarbon, polycarbonate, polyester,polyacrylate, polyether, polyethylene, polyamide, polyurethane,polystyrene, polypropylene, coformed products thereof, and mixturesthereof.

Desirably, the CMP apparatus further comprises an in situ polishingendpoint detection system, many of which are known in the art.Techniques for inspecting and monitoring the polishing process byanalyzing light or other radiation reflected from a surface of theworkpiece are known in the art. Such methods are described, for example,in U.S. Pat. No. 5,196,353, U.S. Pat. No. 5,433,651, U.S. Pat. No.5,609,511, U.S. Pat. No. 5,643,046, U.S. Pat. No. 5,658,183, U.S. Pat.No. 5,730,642, U.S. Pat. No. 5,838,447, U.S. Pat. No. 5,872,633, U.S.Pat. No. 5,893,796, U.S. Pat. No. 5,949,927, and U.S. Pat. No.5,964,643. Desirably, the inspection or monitoring of the progress ofthe polishing process with respect to a workpiece being polished enablesthe determination of the polishing end-point, i.e., the determination ofwhen to terminate the polishing process with respect to a particularworkpiece.

A chemical-mechanical polishing process can be characterized in a numberof ways, such as in terms of the removal rate of a substrate, theresulting surface roughness, and the resulting edge roll-off of asubstrate.

The removal rate of a substrate can be determined using any suitabletechnique. Examples of suitable techniques for determining the removalrate of a substrate include weighing the substrate before and after useof the inventive polishing method to determine the amount of substrateremoved per unit of polishing time, which can be correlated with theremoval rate in terms of thickness of substrate removed per unit ofpolishing time, and determining the thickness of the substrate beforeand after use of the inventive polishing method to directly measure theremoval rate of the substrate per unit of polishing time.

One measure of defectivity is the total scratch count as defined as thesum of shallow, micro, and deep scratches on the surface of a substrateafter polishing. Another measure of defectivity is the count of microparticles that either adhere to the surface or are embedded in thesurface of a substrate that has been polished. The substrate, such as anickel-phosphorous coated memory disk, can be inspected using opticaldefect scanning equipment such as the Candela 6100 and 6300 series andsimilar instruments available from KLA Tencor (Milpitas, Calif.).

Desirably, the inventive polishing composition and method disclosedherein result in reduction in the total scratch count and/or in thecount of micro particles when used to polish substrates comprising anickel-phosphorous coated memory disk.

The following example further illustrates the invention but, of course,should not be construed as in any way limiting its scope.

EXAMPLE

This example demonstrates the effect on defectivity achievable by theinventive polishing composition in the polishing ofnickel-phosphorous-coated aluminum memory disks.

Similar substrates comprising nickel-phosphorous-coated aluminum memorydisks were separately polished on one side with four different polishingcompositions. Each of the polishing compositions comprised 5 wt. % of awet-process silica having an average particle size of ≦30 nm, 1 wt. %glycine, and 0.6 wt. % hydrogen peroxide in water at a pH of 1.9.Polishing Composition A (control) did not contain any polyvinyl alcohol.Polishing Compositions B, C, and D further comprised 250 ppm, 500 ppm,and 1000 ppm of a polyvinyl alcohol, respectively, wherein the polyvinylalcohol had a molecular weight in the range of 13,000-23,000 g/mol and adegree of hydrolysis of about 98%.

Following polishing, the substrates were examined for total scratchcounts, shallow scratch counts, deep scratch counts, micro scratchcounts, and micro particle counts, wherein micro particle counts refersto particles adhered to or imbedded in the substrate surface. Theresults are set forth in the Table.

TABLE A* B C D Composition (control) (invention) (invention) (invention)Total scratch 56 7 12 7 count Shallow scratch 30 5 5 4 count Deepscratch 5 1 1 1 count Micro scratch 22 2 6 3 count Micro particle 925906 584 485 count *average of two experiments

As is apparent from the results set forth in the Table, the inventivepolishing compositions B-D exhibited approximately 79-88% reductions inthe total scratch count, approximately 83-87% reductions in the shallowscratch count, approximately 80% reductions in the deep scratch count,and approximately 73-91% reductions in the micro scratch count, comparedto the control polishing composition A. Inventive polishing compositionsC and D, which contained 500 ppm and 1000 ppm, respectively, ofpolyvinyl alcohol, exhibited approximately 38% and 48% reductions in themicro particle count compared to control polishing composition A.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

The invention claimed is:
 1. A method of chemically-mechanicallypolishing a memory or rigid disk substrate, which method comprises: (i)providing a memory or rigid disk substrate comprising at least one layerof nickel-phosphorous, (ii) providing a polishing pad, (iii) providing apolishing composition comprising: (a) wet-process silica, (b) anoxidizing agent that oxidizes nickel-phosphorous, (c) a chelating agent,(d) polyvinyl alcohol, wherein the polyvinyl alcohol has a degree ofhydrolysis of about 90% or more, (e) water, wherein the polishingcomposition has a pH of about 1 to about 4, (iv) contacting a surface ofthe substrate with the polishing pad and the polishing composition, and(v) abrading at least a portion of the surface of the substrate toremove at least some nickel-phosphorous from the surface of thesubstrate and to polish the surface of the substrate.
 2. The method ofclaim 1, wherein the polishing composition comprises about 1 wt. % toabout 10 wt. % of wet-process silica.
 3. The method of claim 1, whereinthe oxidizing agent is hydrogen peroxide.
 4. The method of claim 1,wherein the chelating agent is glycine or alanine.
 5. The method ofclaim 1, wherein the polishing composition comprises about 0.1 wt. % toabout 2 wt. % of the chelating agent.
 6. The method of claim 1, whereinthe polyvinyl alcohol has a degree of hydrolysis of about 98% or more.7. The method of claim 1, wherein the polishing composition comprisesabout 0.1 wt. % to about 2 wt. % of polyvinyl alcohol.
 8. The method ofclaim 1, wherein the polishing composition has a pH of about 1 to about3.
 9. The method of claim 1, wherein the substrate is anickel-phosphorous-coated aluminum disk.
 10. The method of claim 1,wherein the wet-process silica has an average particle size of about 10nm to about 80 nm.
 11. The method of claim 10, wherein the wet-processsilica has an average particle size of about 10 nm to about 30 nm. 12.The method of claim 1, wherein the polyvinyl alcohol has a molecularweight of about 8,000 g/mol to about 50,000 g/mol.
 13. The method ofclaim 12, wherein the polyvinyl alcohol has a molecular weight of about13,000 g/mol to about 23,000 g/mol.
 14. A method ofchemically-mechanically polishing a memory or rigid disk substrate,which method comprises: (i) providing a memory or rigid disk substrate,(ii) providing a polishing pad, (iii) providing the polishingcomposition comprising: (a) wet-process silica, (b) an oxidizing agentthat oxidizes nickel-phosphorous, (c) a chelating agent, (d) polyvinylalcohol, wherein the polyvinyl alcohol has a molecular weight of about8,000 g/mol to about 50,000 g/mol, (e) water, wherein the polishingcomposition has a pH of about 1 to about 4, and wherein the polishingcomposition does not comprise a heterocyclic compound, (iv) contacting asurface of the substrate with the polishing pad and the polishingcomposition, and (v) abrading at least a portion of the surface of thesubstrate to remove at least some portion of the surface of thesubstrate so as to polish the surface of the substrate.